In this paper we describe mechanisms for execution monitoring of semantic web services, based on OWL-S. The use of semantic descriptions and ontologies is a valuable extension to current SOA conceptualizations. The described mechanisms are implemented as extensions of the OWL-S Virtual Machine that we have previously developed. The OWL-S Virtual Machine is a component that controls the in- teractions between a client and the web service it uses. The presented extensions are a result of practical requirements that arose in the course of involvement with two projects that utilize OWL-S based semantic web services. In partic- ular, we present an event-based model for monitoring and logging interactions. The interaction trace allows a human or software agent to analyze, replay or debug the execu- tion. Additionally, we describe proposed extensions to cur- rent specification in OWL-S for reporting and handling of errors. Finally, we describe extensions to the OWL-S Vir- tual Machine based on introspection to enable dynamic in- teractions with process mediators.